ABSTRACT
Every decision to prevent, or intervene in, a suspected developmental handicap entails implicit assumptions about normal and deviant development. The assumption may be that all essential human attributes are preprogrammed in the genome, so that ontogenesis is only an epiphenomenon (preformationism); or that behavioral development is the near-linear accretion of habits shaped by environmental contingencies, so that biology plays at most a peripheral role (environmentalism). An alternative assumption may be that intrinsic maturational timetables control the course of ontogeny, whereas experience has a triggering, but not an inductive, function (maturationism); or that biology and experience are merely different dimensions of a unitary developmental process that induces novel behavioral forms and operating principles which are not present in either the genome or the environment (epigenetic constructivism).
